Health authorities in the United States and the United Kingdom are alerting hospitals to be on the lookout for an emerging multidrug-resistant yeast in patients that is causing potentially lethal, invasive infections in healthcare settings. First brought to the attention of medical authorities in 2009 in Japan, outbreaks of Candida auris infections have now occurred in nine countries on four continents.

Patients who have been in intensive care for a long time appear to be particularly susceptible to invasive infection by C. auris.

The Centers for Disease Control and Prevention (CDC) in the U.S. and Public Health England (PHE) in the U.K. have issued alerts to hospitals and testing labs warning that healthcare facilities in several countries have reported that C. auris has been causing severe illness in hospitalized patients.

Invasive infection - where the yeast enters the bloodstream - with any Candida species can be fatal. Based on information from a limited number of patients, the CDC note that 60 percent of patients with C. auris infection have died. However, many of them had serious illnesses that, on their own, raised their risk of death.

There are three main reasons to be concerned about C. auris infections, say the CDC. First, it is often multidrug-resistant; second, it is difficult to identify; third, it has caused outbreaks in hospital settings.

C. auris can enter the bloodstream and spread through the body, causing severe invasive infection. It often does not respond to commonly used antifungal drugs, making infections difficult to treat. The yeast can also cause wound infections and ear infections.

Recent emergence of C. auris in different places a mystery

The yeast infection was first identified in 2009 in Japan after being isolated from ear discharge of a patient. Since then, C. auris infections that have entered the bloodstream have been reported from South Korea, South Africa, India, and Kuwait.

Infections have also been identified in Colombia, Pakistan, the U.K., and Venezuela, although these are not detailed in any published reports, note the CDC.

Sporadic cases have been identified throughout England since 2013. One English hospital has identified more than 40 cases in its adult critical care unit.

Two other cases have also been identified in another English hospital, and investigations are under way to find if there are any other cases, says Dr. Berit Muller-Pebody, head of the antimicrobial resistance section at PHE.

So far, however, no multidrug-resistant strains of C. auris have been found in the U.K.

A review of samples collected in the past has raised the possibility of there having been at least one case of C. auris infection in the U.S. that occurred in 2013.

Why C. auris has recently emerged in so many different places is somewhat of a mystery. Molecular analysis of strains suggests while they are related within a country or region, they are highly distinct between continents.

Retrospective testing of samples have revealed that the earliest known infection with C. auris was in South Korea in 1996.

C. auris identification is difficult, risk factors unclear

C. auris can only be identified reliably with molecular analysis; conventional lab techniques can mistakenly confuse it with another related fungus.

Misidentification leads to the wrong treatment and raises the chance of the infection spreading to other patients.

Unlike its cousin C. albicans - the yeast that causes thrush infections in the genitals and mouth - C. auris has also been found in urine and respiratory samples. However, it is not clear whether it causes infections in the lung or bladder.

There is not much data on risk factors for C. auris infections, but the CDC say evidence suggests these are much the same as for other types of Candida infections, including recent surgery, diabetes, use of broad-spectrum antibiotics and antifungals, and use of central venous catheter (catheter in a large vein).

Patients who have been in intensive care for a long time appear to be particularly susceptible.

More work needed to understand C. auris

The CDC note it is unlikely that travel to the countries with known outbreaks of C. auris will increase a person's chance of becoming infected with the yeast, as infections have primarily affected patients who were already in the hospital for other reasons.

Most C. auris infections are treatable with a class of antifungals called echinocandins. However, in some cases, the yeast infections have been resistant to all three main classes of antifungals, making them more difficult to treat. In such cases, the infection is treated with high doses of several classes of antifungal drugs at the same time.

The authorities say more work is needed to understand how C. auris spreads, but early evidence suggests it could be via contact with surfaces or medical equipment, or from person to person.

However, certain infection control measures - such as strict hand hygiene and wearing gowns and gloves - are likely to prevent spread. Thorough environmental cleaning of hospital rooms could also help.

Other measures include screening of patients, isolation of those infected, and temporary closure of affected wards to enable thorough deep cleaning with an approved, fungus-targeting product.

The CDC say:

"C. auris may not represent a new organism so much as one that is newly emerging in various clinical settings. Although the causes for such emergence are unknown, they may include new or increasing antifungal selection pressures in humans, animals, or the environment."

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